Seed viability (percent of germination) of accessions is the most critical factor for seed distribution from the genebank and for new cycles of regeneration. The initial germination test of seed lots of new introductions or seed increased in nurseries is conducted after the seed is dried to the optimal moisture content (6-8%). Once in storage, the first monitoring of seed viability is conducted after ten years of storage in the active collection; then, after every five years as recommended by the standard germplasm bank operation guidelines (FAO/IPGRI 1994).

The wet paper with the seeds is rolled and placed
in germinating trays (photo: CIMMYT)

The determination of germination percent (%) should be performed with seeds that are dried and cleaned. It is recommended to follow the ISTA rule to count the seeds that have normal and abnormal germination after four and seven days to determine the percent of germination.

Type of test

CIMMYT method:

Seeds are scattered in counting boards of various sizes which are placed on wet filter paper (grade S-915-A, 90 g per square meters) of 35 x 17 cm.

The wet paper with the seeds is then rolled and placed in a germinating tray with sufficient water in the bottom. One side of the filter paper is folded with a 1-1.5 cm margin before rolling it up with the seeds.

The folded side of the filter paper is dipped in the water in the tray to help absorb water for germinating seeds.

IITA method:

Germination paper of Seedburo K-22 is effectively used with sterile distilled water.

There are also other ways to set up the seed germination effectively, click here for more information.

Number of seeds and replicates

The seed bank curator should use at least two replicates of 50 seeds per set, depending on the seeds, labour and facilities available.

The chamber temperatures can be monitored by a data logger in the germination room.

Light

12 hours’ light and 12 hours’ dark conditions.

Duration of test

One week.

Other

The accession or introduction ID number and the replicate number should be written on the dry filter paper (substrate for the seed germination) with a thick lead pencil (Design Ebony) or other types of markers for identification of the seed lots.

The seedlings should be evaluated on the substrate on the 4th day and 7th day, counting normal, abnormal seedlings and un-germinated seeds .

When there is a large difference between replicates in terms of germination percentage, then a second test should be done to confirm the results.

This routine checks are very important to maintain the genebank operation in perpetuity. The seed accessions should be constantly available to the users.

Methods

The genebank curator should regularly monitor seed quantity and seed viability, in addition to ensuring the storage conditions (relative humidity and temperature) of the seed vaults.

Safety from vandalism and robbery should also be monitored in the genebank’s operations.

The curator should monitor the inventory of the seed accessions for percentage of germination once a year.

Percentage of germination should be updated in the genebank database management system when the seed accessions are utilized.

When percentage of germination falls below critical levels (85%), seed should be regenerated.

The germplasm accessions that are well-adapted to the regeneration sites can be readily regenerated and seed increased.

The accessions not adapted at the genebank’s regeneration sites need a special arrangement with the collaborating genebanks that can regenerate them (consult the Regeneration guidelines for maize for more details).

Monitoring intervals

Routine monitoring is necessary to ensure viability of seed accessions in both the base and active collections. It is important that seeds be constantly available to users.

Seed viability should first be monitored after ten years of storage with subsequent monitoring at intervals of 5-10 years. It should be noted that seed viability in the base collection is expected to last longer than that in the active collection and thus monitoring intervals can be longer.

Critical germination level

Seed viability is necessary to ensure a sufficient sample size of accessions for the maintenance of genetic integrity over many regeneration cycles. Seed viability is critical to avoid a population bottle neck of accessions during storage.

The critical germination level is set at 85%, based on the initial seed viability of 100%..

The germination of older seeds in the field is expected to be lower (as low as 50%) that the germination percentage revealed by viability testing.

It is preferable to regenerate the germplasm accessions before reaching a percentage of germination as low as 65%.

In the case of inbred lines, germplasm should be regenerated before seed viability falls below 80%.

FAO/IPGRI. 1994. Genebank standards. Food and Agriculture Organization of the United Nations, Rome and International Plant Genetic Resources Institute, Rome. Available in English, Spanish, French and Arabic.